In charcopyrite-based thin film solar cells, N-type buffer layer is conventionally prepared by chemical bath deposition (CBD) without additional treatment. The buffer layer is deposited on the absorber layer and impurities such as oxide or other particles would be directly coated by buffer layer. A ZnO layer is deposited over the buffer layer and after ZnO deposition and lamination, those impurities would result in poor adhesion between the absorber and buffer layer, thereby causing delamination.
Additionally, during CBD process, sodium-based compounds leaching out of the glass substrate along the scribe lines diffuse through the absorber layer and tend to concentrate along the scribe lines. This induces formation of large particulate impurities on the CIGS absorber layer along the scribe lines. Those particles are detrimental to performance of the chalcopyrite-based solar cells as well as their appearance.
After selenization or sulfurization, a thin oxide layer often forms on the surface of absorber layer. This oxide layer degenerates quality of p-n junction, therefore resulting in a decrease of efficiency of cell.